Mycorrhizal growth and phosphorus responses of tropical soybean (Glycine max L.) cultivars differ with arbuscular mycorrhizal fungi isolates and phosphorus application rates in a derived-savanna zone of Nigeria

Arbuscular mycorrhizal fungi (AMF) form symbiosis with most crops and provide a sustainable approach to promote crop productivity in phosphorus (P) deficient soils. There is scarcity of information on mycorrhizal growth and P responses in relation to different AMF isolates, P rates and soybean cultivars in Nigeria. Thus, field experiments were conducted for two consecutive years (2017 - 2018) to explore the impacts of different AMF isolates (Funneliformis mosseae, Rhizophagus intraradices and Claroideoglomus etunicatum) and P application rates (0, 20 and 40 kg P2O5 ha(-1)) on plant growth, mycorrhizal responses, nodulation, P nutrition and grain yield of two soybean cultivars (TGx 1448-2E and TGX 1440-1E). The results showed that mycorrhizal inoculation significantly enhanced root colonization, shoot biomass, nodulation, P uptake, P use efficiency and grain yield of the soybean cultivars compared to control. Inoculation of R. intraradices and F. mosseae consistently favored mycorrhizal responses compared to C. etunicatum. Application of high P rate (40 kg ha(-1)) negatively affected root colonization, mycorrhizal growth and P responses in inoculated plants. Both cultivars showed similar mycorrhizal responses. Mycorrhizal growth and P responses were significantly enhanced with inoculation of R. intraradices or F. mosseae and P rate of 20 kg ha(-1), which resulted in increased P uptake, shoot biomass and grain yield in both cropping years . The findings indicated that inoculation of R. intraradices or F. mosseae with moderate P rate (20 kg ha(-1)) is optimal to promote plant growth, P nutrition and grain yield of tropical soybean for sustainable cultivation in Nigeria.